[sugar] Implicit saving

The implicit saving on activity close gets in the way of how etoys
traditionally worked. If I create, say, a simulation, I will arrange
everything and then save that project, so when I later open it for
demonstration, it is in a state ready to be started. But when I then
run the simulation and quit, it will not be in the ready-to-run state
anymore.
Any idea how that problem should be tackled in Sugar?
- Bert -